Earnings before Income Taxes (Detail) - USD ($) $ in Thousands		12 Months Ended
		May 31, 2017	May 31, 2016	May 31, 2015
Schedule of Income Before Income Tax [Line Items]
United States based operations		$ 266,222	$ 180,467	$ 104,732
Non - United States based operations		30,905	36,148	8,296
Earnings before income taxes	[1]	297,127	216,615	113,028
Less: Net earnings attributable to noncontrolling interests		13,422	13,913	10,471
Earnings before income taxes attributable to controlling interest		$ 283,705	$ 202,702	$ 102,557

[1] Net earnings attributable to noncontrolling interests are not taxable to Worthington.